Date: Thu, 8 Jan 2009 08:57:57 -0500
Reply-To: "Hadden, Susan [PRDUS]" <SHADDEN**At_Symbol_Here**ITS.JNJ.COM>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: "Hadden, Susan [PRDUS]" <SHADDEN**At_Symbol_Here**ITS.JNJ.COM>
Subject: Summary- Stents near Magnets

I thought this might be of interest to the group. 

-----Original Message-----
From: Morton, Martha [mailto:martha.morton**At_Symbol_Here**]
Sent: Wednesday, January 07, 2009 11:23 AM
To: ammrl**At_Symbol_Here**
Subject: AMMRL: Summary- Stents near Magnets

Dear ALL,
The general consensus is stent wearers should stay out of the 5G lines 
at least for year, while the stent "grows" in.  All people wearing 
stents should consult the vendor and /or their physician.  Certain 
stainless steel might be okay, but this depends on how the stent is 
inserted.  The two concerns about stents include movement of the stent 
and eddy currents causing local heating and therefore increased drug 
release, if the stent is coated or burns.  One survey of people, who 
wore stents, but still had MRIs, showed little or no movement of the 
stent.  This could be time related as there is a "grow" in time.  I've 
added some of your helpful summaries below.
Thank you to all of you,
Nearly 4 years ago I had a stent fitted in my right coronary artery 
following a heart attack - from what you've said it sounds like the same 
type of stent, a drug eluting one. These are relatively new tech, when I 
explained my work with powerful magnets to my consultant he stated that 
' he didn't have figures for the drug eluting stents, but that typically 
a normal stent would be expected to have 'grown in' to the epithelial 
cells after 6 months - making the stent safe for MRI. In my case he 
erred on the side of caution and banned me from anywhere closer than the 
5 Gauss line for a year!
Since then - nearly 3 years now - I have regularly been in close 
proximity to all our magnet systems (I guess the most intense field I've 
experienced is probe changes on our 400 & 500 systems) - so far the 
stent hasn't dislodged, and barring initial trepidation, no adverse 

I'm not sure whether this helps or not, but our safety document has a
general statement saying that Objects and people at risk from the
magnetic field are considered safe outside the 5 gauss line (i.e. in
magnetic fields smaller than this). 

For any mechanically activated implant (e.g. pacemaker) this is
important in order for it to be able to operate correctly.  For
"passive" implants the risk in the magnetic field is of it being moved
or dislodged.  Certainly 5 gauss would be safe, but it is likely that
higher magnetic fields would be fine.  The only relevant article that I
found on the internet was the one attached.  This information is
obviously specific to the device used. 
   (I found this link 
particularly helpful.)

I would recommend that the user should contact the manufacturer of the
stent, and ask them for a guideline of field strength that it is safe to
be within.  Once he has this information, if it is one of our magnets,
we would be able to provide him with a plot of the "safe field" region.
About the thing below.....the stent should be made of 316 so not 
magnetic but apparently the concerns with coated stents and MRI's is: 
stent migration (especially after its just been put in), localised 
heating which will increase the elution rate of the rapamycin from the 
stent and the stent causing artifacts in the MRI. Obviously the last is 
not an issue for NMR but the first two may be a concern. However these 
probably won't be an issue after a while once all the rapamycin is gone 
and the artery has healed. But best thing to do is contact the stent 
manufacturer (its probably a Johnson & Johnson Cypher stent?) for their 
If he cannot have an MRI, then he cannot go near the NMR magnets, which 
are at much higher field.  How close he can get to the magnet is a 
matter of opinion. 

We recently heard a medical doctor claim that a stent should be okay 
because it's 'nonmagnetic' but he immediately added that he wasn't 
certain.  The problem is that 'non-magnetic' stainless steel becomes 
magnetic if it's worked (drilled, shaped, etc).  The stent is inserted 
into the body in a collapsed state and then reshaped to form a cylinder 
by inflating a balloon inside the stent.  This reshaping increases the 
magnetic moment by at least an order of magnitude.  The only way to make 
it 'nonmagnetic' again (actually with a very low magnetic moment) is to 
anneal it and the human body is not compatible with the annealing 
temperature!   Don't go near the magnet if you have a steel stent inside 
your body.
You need more information. The statement that he can not have an MRI
could stem from a variety of things. It could be that the applied RF
will heat the stent causing burns. It may be that the stent, while
nonmagnetic enough that the forces are minimal, it may cause huge
distortions  in the image. It may be the stent is magnetic. This
last case is the one that concerns you. My guess (and only my guess)
is that he can not have an MRI because of the RF. You should find out
the variety of Stainless Steel to find out if it is magnetic. Some
Stainless Steels are and some are not. In particular 300 series (304,
316, 321, etc.) Stainless Steels are not magnetic.
Martha Morton, Ph. D.
University of Connecticut NMR Facility Scientist
Chemistry NMR Lab Director

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